BRITAIN: C's Busted Cover

The director of Britain's Secret
Intelligence Service, popularly known as M16, has always been referred
to by his in-the-know colleagues as "C." The practice is said to date
back to the department's first director, Sir Mansfield Gumming, who
insisted on it for the sake of anonymity. Sir Mansfield, who died in
1923, passed the initial on to his successors. To the British press, on
the other hand, the director of M16 is usually referred to as "M"as
in the James Bond thrillers.